Zeuxo seurati ( Nobili, 1906 )

Bird, Graham J., 2019, Tanaidacea (Crustacea: Peracarida) from the Southern French Polynesia Expedition, 2014. I. Tanaidomorpha, Zootaxa 4548 (1), pp. 1-75 : 47-56

Zeuxo seurati ( Nobili, 1906)

( Figs 23–29 )

Tanais Seurati : Nobili (1906): 266; Nobili (1907): 413, plates II figs 16, 16a, III figs 1, 1a.

Tanais seurati : several, see Sieg (1980): 221; Anderson (2016): 722.

Anatanais seurati: Stephensen (1936) : 371.

Anatanais insularis : several, see Sieg (1980: 221; Anderson (2016): 722 –723; non Tanais seurati Nobili, 1906 .

Zeuxo (Parazeuxo) seurati ( Nobili, 1906) : Sieg (1980): 221 –225, figs 62, 64, non Tanais seurati Nobili, 1906 .

Zeuxo seurati : several, see Anderson (2016): 722.

Material examined. Holotype— female, one microslide with antennule, mouthpart bundle (only right mandible clearly visible), and partial uropod, plus wet remnant of whole specimen in poor condition (“defekt” according to Sieg 1980: 221; not seen); MNHN Ta.37, from ulvaceous algae on buoy, Banc Gaveau (reef), Mangareva, Gambier Islands, 27 January 1904, coll. G. Seurat.

Other material —AUSTRAL ISLANDS: one ov. ♀ P. 102355, Stn 16-7; three non-ov. ♀♀, one prep. ♀ P. 102354, Stn 18-3; one prep. ♀, cop. ♂ P.98948, Stn 36-1; one non-ov. ♀, one prep. ♀ P. 102357, Stn 54-2; one cop. ♂ P. 102353, Stn 54-5.

GAMBIER ISLANDS: one non-ov. ♀, two ov. ♀♀, one prep. ♂, one cop. ♂ MA124694, one prep. ♀ P. 102366, Stn 66-3; one non-ov. ♀, one prep. ♀ P. 102365, Stn 66-4; one prep. ♂ P. 102352, Stn 66-5; one prep. ♀, one cop. ♂ P. 102358, ten non-ov. ♀♀, five prep. ♀♀, eleven ov. ♀♀, 17 prep. ♂♂, one cop. ♂ P. 102359, one prep. ♀ dissected on two microslides P. 102360, P.102360.001, one prep. ♀ with pleon dissected on microslide P. 102361, P.102361.001, one prep. ♂ chelipeds dissected on microslide P.102362.001, one cop. ♂ partly-dissected residue P. 102363 (slide lost), Stn 66-A; one non-ov. ♀?, two ov. ♀♀ P. 102356, non-ov. ♀ P.99217, Stn 68-3.

MORANE: non-ov. ♀, prep. ♀, ov. ♀, prep. ♂, cop. ♂ MA124695, prep. ♂ P. 102364, Stn 64-2.

Diagnosis. Female: Zeuxo with antennule article-1 2.6 times longer than article-2; article-4 with three aesthetascs. Mandibles with left lacinia subconical, with small accessory spine; right mandible lacinia small, acuminate. Pereopod-1 coxa with acuminate spur twice as long as broad, with three setae. Pereopods 2–3 carpus with six crotchets, longest less than half as long as propodus. Pereopods 4–6 merus with two superodistal (tergal) setae, carpus with eight crotchets. Pleopod peduncle with one mesial and six lateral plumose setae; endopod with two proximomesial plumose setae. Uropod four- to six-segmented, plus peduncle (mature specimens).

Male: as female but slightly dimorphic. Antennule with seven or eight distal aesthetascs. Cheliped more massive; fixed finger superior margin straight but with raised incisive edge. Uropod five-segmented.

Type locality. Banc Gaveau reef (on buoy), Mangareva, Gambier Islands, French Polynesia (c. 23° 08' 26" S 134° 58' 27" W) . “ Neotype ” locality: Taravai , Gambier Islands , 23° 07' 51" S 135° 02' 05" W, rubble, 10–16 m.

Redescription. Preparatory female, 3.2 mm (P. 102358). Habitus ( Fig. 23A ) fairly slender, 6.1 times ltb; pigmented brown on cephalothorax, pereonites 2–6, pleonites, and pleotelson. Cephalothorax just shorter than pereonites 1–3 combined, 1.2 times ltb; carapace with distolateral setae; setae of coxal sclerite and cheliped basis also visible from dorsal view. Pereon 4.2 times ltb, with pereonite-1 shortest, pereonites 2–3 subequal, pereonites 4–5 longest, pereonite-6 narrower than pereonite-5; all with dorsolateral and posterolateral setae. Pleon ( Fig. 23A– C ) as long as pereonite-6 and half of pereonite-5 combined; pleonites 1–3 with several lateral-epimeral plumose setae (ca. four, five and four respectively), pleonites 1–2 also with group of dorsolateral plumose setae (five and three respectively), and pleonites 1 and 3 with dorsolateral simple seta; pleonites 4–5 very short, with one and two unequal lateral setae respectively (per margin). Pleotelson ( Fig. 23A, C ) 0.5 times as long as broad, with two unequal posterolateral setae and three unequal posterodorsal setae and one PSS (per margin), and four apical setae, outer pair longer.

Preparatory female, 3.4 mm (P. 102360, P.102360.001). Antennule ( Fig. 23D ) 0.7 times length of cephalothorax, 4.5 times ltb overall; article-1 57% of total length, 2.9 times ltb, and 2.6 times longer than article-2; article-2 1.6 times ltb; article-3 0.8 times length of article-2; article-4 very short, with three aesthetascs; other setation as figured. Antenna ( Fig. 23E ) article-2 about 1.5 times ltb, with dorsodistal seta, and two ventrodistal setae; article-3 as long as broad, naked; article-4 1.25 times length of article-2, with three distal setae and PSS; article-5 0.8 times length of article-4, with three distal setae and four PSS; article-6 just longer than broad, with distal corona of six long setae; article-7 very small, with five long setae and one PSS.

Mouthparts. Labrum ( Fig. 24A ) typical, hood-like; densely setulate. Mandibles ( Fig. 24B–C ) left mandible ( Fig.24B ) lacinia subconical, with small acuminate accessory spine; right mandible ( Fig. 24C ) lacinia small, spiniform. Labium ( Fig. 24D ) typical; both lobes distally setulate, outer lobe with small setulate palp. Maxillule ( Fig. 24E–F ) endite with distal combs and setules, with at least eight terminal spines (one thinner than rest); palp with three apical setae. Maxilla not observed.

Maxilliped ( Fig. 24G–I ) typical, coxa with two setae; bases together 1.3 times ltb, each with lateral margin setulate and one distal seta. Endite distally setulate, with two medial coupling hooks, two large distal pinnate setae and two smaller (oral) setae. Palp article-1 with lateral seta; article-2 with lateral seta and nine mesial and distomesial smooth (or very finely serrulate) setae; article-3 with two rows (ten and six) mesial setae; article-4 with subdistal seta and about ten distal setae. Epignath ( Fig. 24J ) typical, linguiform,, apex with setulate process.

Cheliped ( Fig. 25A–B ) coxal sclerite with two unequal dorsal setae; basis posterior lobe as large as anterior mass, latter with dorsodistal seta and ventrodistal seta; merus ventral margin 1.4 times longer than that of carpus, with two ventral setae and two dorsolateral setae near articulation with basis; carpus 1.6 times ltb, dorsal margin with one seta at midlength and distal group of three unequal setae, ventral margin with five unequal setae. Chela longer but narrower than carpus, 2.2 times ltb; palm with mesial spine ( Fig. 25B ) and four lateral setae near articulation with dactylus; fixed finger with five ventral setae, two distomesial setae and six lateral setae near incisive margin, incisive margin with raised laminar distal apophysis; dactylus with mesial seta, and ventral margin with row of small spines.

Pereopod-1 ( Fig. 26A–B ) coxa with acuminate spur about twice as long as broad, with three setae; ischio-basis 4.4 times ltb, superoproximal margin with one simple seta and one PSS and inferodistal seta; merus 1.4 times ltb, with single supero- and inferodistal setae; carpus subrectangular, 1.5 times longer than merus, 2.2 times ltb, with one superodistal and two inferodistal setae; propodus length of merus and carpus combined, 4.5 times ltb, tapering, with superior simple seta and small PSS, long distomesial seta, and four unequal inferodistal setae; dactylus shorter than unguis, with small proximal seta, together 0.7 times length of propodus.

Pereopod-2 ( Fig. 26C–E ) coxa simple, with seta; ischio-basis broader than in pereopod-1, 3.2 times ltb, with superoproximal simple seta and small PPS, inferodistal margin with three setae; merus geniculate, twice length of broad, with superodistal seta, three inferodistal setae, inferodistal (lateral) crotchet and numerous microtrichia; carpus 0.6 times length of merus, 1.3 times ltb, with superodistal seta, two inferodistal setae, six crotchets and numerous microtrichia; propodus 0.7 times as wide as carpus, 1.5 times longer, with superior PSS, two superodistal setae (one small) and three unequal inferodistal setae; dactylus with accessory seta, together with unguis 0.6 times length of propodus.

Pereopod-3 ( Fig. 26F ) like pereopod-2 but ischio-basis slightly shorter; merus slightly shorter, 1.7 times ltb; carpus with one inferodistal seta; propodus with two inferodistal setae.

Pereopod-4 ( Fig. 26G ) ischio-basis broader than in pereopods 2–3, 2.6 times ltb, with one subdistal inferior PSS and three inferodistal setae; merus geniculate, twice as long as broad, with two unequal superodistal setae, three inferodistal setae, two inferodistal crotchets, and numerous microtrichia; carpus 0.75 times length of merus, 1.4 times ltb, with two superodistal setae, eight distal unequal crotchets, and numerous microtrichia; propodus about length of carpus, narrower and slightly arcuate, twice as long as broad, with superodistal PSS, one inferior seta, two long distal setae and two inferodistal setae; dactylus and unguis claw-like, dactylus with proximal spinules, unguis with double comb of 6–7 spines.

Pereopod-5 ( Fig. 26H ) like pereopod-4 but ischio-basis with a superoproximal PSS subdistal inferior PSS and simple seta, and merus with two inferodistal setae.

Pereopod-6 ( Fig. 26I ) like pereopod-5 but ischio-basis with one superoproximal PSS; propodus with distolateral fringe of ten blade- or leaf-like spines.

Pleopod ( Fig. 26J ) peduncle 1.25 times ltb, mesial margin with one plumose seta, lateral margin with six plumose setae; endopod 2.1 times ltb, mesial margin setulate, with two proximal plumose setae; lateral margin with fringe of 15 setae, distalmost short and thick, with whip-like tip; exopod longer and wider than endopod, 2.1 times ltb, with lateral fringe of 26 plumose setae.

Uropod ( Fig. 23F ) peduncle 2.6 times ltb, with six distal setae (two groups of three); setation as figured.

Intraspecific variation. Manca-III habitus much stouter than female, w ith rudimentary pereopods-6 and pleopods; length 0.97 mm (n=1). Antennule article-4 with one aesthetasc. Uropod with three-segmented endopod.

Non-ovigerous female/neuter. Essentially like female; length 1.4–3.7 mm (n=25). Antennule article-4 with two or three aesthetascs (mostly three). Uropod endopod 3–6 segmented (related to body length).

Preparatory and ovigerous female. Habitus similar to holotype; length 2.1–3.4 mm (preparatory, n=16), 2.3– 3.8 mm (ovigerous, n=20). Uropod endopod 4–6 segmented (but those with four-segmented have the other uropod five-segmented), predominantly five-segmented.

Preparatory male. Habitus like female or neuter progressively to copulatory male; length 1.6–2.3 mm (n=25). Pereonite-6 sternum with slightly raised, paired genital cones. Paratype preparatory male (P.102362.001). Antennule ( Fig. 25C, F ) article-4 with 5–10 aesthetascs. Cheliped ( Figs 25D , 27A ) as female or progressively like copulatory male. Uropod ( Fig. 25E, G ) endopod four- or five-segmented.

Copulatory male, 2.3 mm (P. 102358). Habitus ( Fig. 27B ) fairly stout, 5.3 times ltb. Cephalothorax proportionately slightly larger than female. Pereon stouter than female, 3.1 times ltb (allotype). Pleon similar to female, pleonite-1 with one simple and five dorsolateral setae, pleonite-2 with five lateral and three dorsolateral plumose setae, and pleonite-3 with one simple dorsolateral seta and four lateral plumose setae. Pleotelson similar to female. Genital cones more elevated than in preparatory male.

Copulatory male, 2.4 mm (P. 102363): Antennule ( Fig. 27C–D ) slightly longer and more slender than in female, 0.9 times length of cephalothorax, five times ltb overall; article-1 3.2 times ltb, three times longer than article-2; setation similar to female but terminal article with seven or eight aesthetascs.

Cheliped ( Fig. 27E–F ) larger and stouter than female; sclerite with two dorsolateral setae; basis just shorter than broad; merus with two dorsolateral setae and two ventral setae; carpus 1.5 times lth, with three ventral setae, one dorsal seta and dorsodistal group of three setae; chela longer but narrower than carpus, 2.4 times lth, palm with single mesial seta; fixed finger triangular, with three lateral setae adjacent to dactylus, four ventral, two distomesial, and seven dorsal (incisive margin) setae, the last arising from a longitudinal ridge, terminal spine short; dactylus arcuate, attached anaxially, ventral margin with proximal apophysis with three spinules and several distal spinules, unguis short.

Uropod as in female, five-segmented.

Body length of other copulatory males 2.1–2.4 mm (n=6).

Distribution and habitat. Recorded from all three island groups—Austral, Gambier and Morane, intertidal to 28 m, although most are from sublittoral sites. It was sampled from a variety of substrates, namely coral rubble, the green alga Halimeda , an ascidian, and finely-branched coral.

Remarks. The only Zeuxo species to have been recorded from the Polynesian region is Z. seurati , which until now included the synonym Anatanais insularis Miller, 1940 . However, the redescription of Z. seurati ( Sieg 1980: 221–225, fig. 62) was based on two females of the Hawai’ian A. insularis (it appears that Sieg did not examine the holotype) as well as the Tanais seurati holotype. It was only assumed by Sieg to be conspecific with Nobili’s T. seurati from “Touamotou”, whose holotype is in a poor condition (“defekt”, Sieg 1980: 221), possibly because of the vague Polynesian link, and the similarities of the mandible and pereopod-2. These two characters are valid but in themselves neither diagnostic nor confirmatory. Even when first described, the holotype was missing the right cheliped, and Nobili (1906) only illustrated pereopods 5–6 (as well as the whole specimen and a uropod). The existing type material of Tanais seurati consists a worthless wet specimen of the whole body, and two microslides displaying a whole antennule, a bundle of mouthparts of which only the right mandible is visible, and two distal segments of a uropod.

Because the type locality of T. seurati is just off the southern coast of Mangareva (on the Banc Gaveau reef) and only c. 6.5 km from the new Taravai site ( Fig. 28 ), it is determined that the species redescribed here is Zeuxo seurati sensu Nobili, 1906 , rather than Zeuxo insularis ( Miller, 1940) n. comb. from Hawai’i, c. 5000km to the northwest

As with the very similar Z. kermadecensis Bird, 2015 , Z. seurati s.s. would fit the diagnosis for the subgenus Zeuxo (Zeuxo) ( Sieg 1980: 190) rather than Zeuxo (Parazeuxo) for Z. seurati sensu Sieg (1980) = Zeuxo insularis . Individuals of Z. seurati from Morane, the Gambier and Austral Islands appear to be similar. Having fivesegmented uropods (also reported by Nobili) makes it the seventh of the 13 described Zeuxo (Z.) species with this feature, and the fourth to lack an accessory seta on the right mandible and with a simple spine on the left.

Typically, some individuals of Z. seurati have an unequal number of uropod segments or nearly-formed segments, and this feature is distinctly allometric and stable only in sexually mature individuals (or those of comparable size). This also applies to the number of antennular aesthetascs. The body-size versus uropod-segment count of Z. seurati , compared with the similar Z. kermadecensis , is shown in Figure 29A . Compared to Z. kermadecensis , Z. seurati also has a proportionately slightly smaller cephalothorax re body length, i.e. a linear coefficient of 0.17 against 0.23, and more numerous leaf-like spines in the distal comb on the propodus of pereopod-6, i.e. ten versus seven. Table 8 summarises several variant morphological characters among Indo-Pacific species of Zeuxo .

Figures

FIGURE 23. Zeuxo seurati preparatory female (P.102358). A, habitus (pigmentation similar to male, Fig. 27B); B, pleonites 1– 3 lateral setation; C, pleotelson. Preparatory female (P.102360, P.102360.001). D, antennule; E, antenna; F, uropod. Scale bars: habitus 1 mm, others 0.1 mm.

FIGURE 24. Zeuxo seurati preparatory female (P.102360, P.102360.001). A, labrum; B–C left and right mandibles respectively; D, labium; E, maxillule endite; F, maxillule palp; G, maxilliped (one palp omitted for clarity); H, maxilliped palp articles 3–4; I, maxilliped palp article-3 inner (oral) setae; J, epignath. Scale bars: 0.1 mm.

FIGURE 25. Zeuxo seurati preparatory female (P.102360, P.102360.001). A, cheliped; B, left chela. Preparatory male (1.96 mm body length). C, antennule (setae omitted); D, cheliped; E, uropod (setae omitted). Preparatory male (2.28 mm body length). F, antennule (setae omitted); G, uropod (setae omitted). Scale bars: 0.1 mm.

FIGURE 26. Zeuxo seurati preparatory female (P.102360, P.102360.001). A, pereopod-1; B, pereopod-1 coxa; C, pereopod-2; D, pereopod-2 carpus obscured (mesial) crotchets; E, pereopod-2 claw; F–I, pereopods 3–6 respectively, with details of obscured carpal crotchets; J, pleopod-1 (all setae plumose, many omitted for clarity). Scale bars: 0.1 mm.

FIGURE 27. Zeuxo seurati preparatory male (P.102362.001). A, cheliped. Copulatory male (P.102358). B, habitus. Copulatory male (P.102363). C, antennule; D, antennule article-2 ventral setae; E, cheliped; F, left chela (lateral and ventral setae omitted). Scale bars: habitus 1 mm, others 0.1 mm.

FIGURE 28. Zeuxo seurati type locality (red marker) and two SFPE-2014 sites on Mangareva (yellow marker) and Taravai (green marker), latter site with Zeuxo seurati.

FIGURE 29. Comparison of body size with number of uropod articles. A, Zeuxo seurati and Z. kermadecensis; data points for Z. kermadecensis slightly displaced on y-axis for clarity; non-integer values indicate specimens with uropods of different segment count. B, Zeuxoides rapaitii and Z. rimuwhero; data points for Z. rimuwhero slightly displaced on y-axis for clarity.